The invention relates to a device for separating solids from liquids by means of flotation, particularly for separating impurities and ink particles from fibre suspensions, with several injectors, which are provided inside a flotation cell.
Deinking flotation is a mechanical process for separating impurities and ink particles from fibre suspensions, particularly those produced in waste paper treatment. This process is linked to generating a suitable amount of gas bubbles over an appropriate range of bubble sizes. By changing the gas-liquid flows and the distribution of bubble sizes, ores, etc. can also be separated from low-grade, unusable material. A similar principle is applied in solid-liquid separation, e.g. in waste water.
Hydrophobic solids or such solids as ink particles or stickies (e.g. also coal as accept material) that have been made hydrophobic by applying surface-active substances are carried to the surface of the liquid by the gas bubbles adhering to them and can then be removed there as foam.
In the pulp and paper industry, this method of using self-priming injectors—mainly comprising a propulsion jet nozzle, mixing pipe or impulse exchange chamber and diffuser—has proved successful in generating gas bubbles and mixing them into the pulp suspension. These individual diffusers are usually assembled in small, round diffuser units (up to 12 individual diffusers). At the exit from the diffuser used for energy recovery a fibre stock bubble dispersion forms.
Processes of this type are known in numerous geometric modifications, e.g. from DE 41 16 916 C2, EP 0 211 834 B1 or AT 408 957, and have reached a high technical standard. Nevertheless, two disadvantages arise when using this process in large-scale industrial applications:
The suction effect of the known diffuser units suffers negative influence if there are eight injectors per unit or more because some of the injectors on the inside have a shorter supply of gas due to the injectors surrounding them. As a result of this short supply, there is a lower overall gas loading, which can lead to the propulsion jet being scattered. This reduces the operating reliability and/or the desired distribution of bubble sizes widens, which leads to a drop in efficiency in selective flotation or to higher losses.